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How To: DIY CO2 Regulator

CO2 regulator systems often cost more than $200, which is a hefty price to pay for a college student. I have a 30-gallon aquarium that is heavily planted, and I would like the plants to grow faster and with less algae and brown spots. Because plants absorb the CO2 in the water to grow, adding more CO2 should fix that problem. So, I’ve decided to attempt to make a CO2 regulator that is loosely based on this Instructable that uses yeast, sugar, and a liter bottle to make a CO2 regulator.


DIY CO2 Regulator materials! Yeast, a liter bottle, sugar, silicone, and tubing.
Total Cost: $20.00-$25.00

*Normal airline tubing can be used, but the CO2 type decomposes slower and has minimal leakage


  Step One  

DIY CO2 Regulator. First step poke a hole into the cap.
Make a hole in the bottle cap.

Make a hole in the center of your bottle cap that is just a tad bit smaller than your tubing. You can use scissors, a nail, or a drill to do so.

  Step Two  

On one end of your airline tubing, make a slanted cut. This will make it easier to fit the tubing through the bottle cap.

  Step Three  

Cut your tubing at an angle and thread it through the hole.
Cut your tubing at an angle and thread it through the hole.

Thread the slanted end of the airline tubing 1.5-2” into the cap with the longer side being on the top part of the cap.

  Step Four  

Seal the tubing with silicone.
Seal the tubing with silicone.

Seal the tube and the cap together using aquarium grade silicone. I also put silicone inside the cap, as well. This allows no air or CO2 to escape from the system once it is up and running. It can take up to 48 hours for the silicone to become fully sealed.

  Step Five  

Final product outside the tank.
The bubble counter catches excess yeast.

At this point, you have a few options. You can either add a bubble counter, a check valve, or neither. In the final product, you can see that I’ve added a bubble counter which minimizes the amount of yeast that enters the tank. Before I added it, the water would get a bit cloudy around the diffuser, and the tubes would get clogged and need to be cleaned. Now, the yeast falls to the bottom of the bubble counter and only the CO2 continues on to the fish tank. On the other hand, a check valve basically does not allow water to flow backwards through the system, but it is not required if you set the system up correctly. If you don’t mind a little yeast in your aquarium or aquarium water in your yeast system, neither of these absolutely need to be added.

  Step Six  

Attach the other end of the tube to an air diffuser. I also did not get a chance to photograph this step, but you can see what it looks like in the final image.

  Step Seven  

Fill bottle half way with lukewarm water.
Fill bottle half way with lukewarm water.

Fill the liter bottle halfway with warm water. It is important that the water is warm because it activates the yeast once it is added. However, the water also cannot be hot because hot water will kill the yeast cultures. If the water is too hot to touch, it will be too hot for system, as well.

  Step Eight  

Add sugar into the water.
Add sugar into the water.

Pour about a cup of sugar into the lukewarm water, and shake it until the sugar dissolves into the water.

  Step Nine  

Add a packet of yeast to the water.
Add a packet of yeast to the water.

Put one packet of yeast into your lukewarm water and gently shake the bottle to mix it, as well. The instructions called to add baking soda which apparently helps the CO2 levels stay more constant, but I didn’t have any on hand.

  Step Ten  

Screw the cap on with the tube and place the diffuser in your tank. It should start bubbling within a day or two and last a couple of weeks.

  Final Product  

DIY CO2 Regulator inside my aquarium.
Final product inside the tank.

For the most part, my CO2 regulator system seemed to work perfectly. It released a steady stream of CO2 for at least a few weeks before running out. The only downside was emptying and smelling the yeast bottle afterwords. I would highly recommend this setup as a way to keep your plants nice and healthy without breaking the bank.